Abstract
In this work, a comparative study about the incorporation of silver nanoparticles (AgNPs) into thin films is presented using two alternative methods, the in situ synthesis process and the layer-by-layer embedding deposition technique. The influence of several parameters such as color of the films, thickness evolution, thermal post-treatment, or distribution of the AgNPs along the coatings has been studied. Thermal post-treatment was used to induce the formation of hydrogel-like AgNPs-loaded thin films. Cross-sectional transmission electron microscopy micrographs, atomic force microscopy images, and UV-vis spectra reveal significant differences in the size and distribution of the AgNPs into the films as well as the maximal absorbance and wavelength position of the localized surface plasmon resonance absorption bands before and after thermal post-treatment. This work contributes for a better understanding of these two approaches for the incorporation of AgNPs into thin films using wet chemistry.
Highlights
The development of nanostructured advanced materials based on the incorporation of metal nanoparticles has attracted the attention of the researchers [1,2,3,4,5]
In situ synthesis process of the silver nanoparticles The weak polyelectrolyte nature of the poly(allylamine hydrochloride) (PAH)/PAA matrix makes the pH of the polyelectrolyte dipping solutions determine the number of free carboxylic acid present in the multilayer thin film
The PAA polyanion presents carboxylate and carboxylic acid groups at a suitable pH where the carboxylate groups are responsible for the electrostatic attraction with the cationic groups of the polycation (PAH), forming ion pairs to build sequentially adsorbed multilayers in the LbL assembly
Summary
The development of nanostructured advanced materials based on the incorporation of metal nanoparticles has attracted the attention of the researchers [1,2,3,4,5]. The optical spectra of the metal nanostructures show an attractive plasmon resonance band, known as localized surface plasmon resonance (LSPR), which occurs when the conductive electrons in metal nanostructures collectively oscillate as a result of their interaction with the incident electromagnetic radiation [6,7] Such nanoplasmonic properties of the metal nanostructures are being investigated because of their unique or improved antibacterial, catalytic, electronic, or photonics properties [8,9,10,11,12,13,14,15]. The high versatility of the poly (acrylic acid, sodium salt) (PAA) has been demonstrated as a protective agent of the silver nanoparticles because of the possibility of obtaining multicolor silver nanoparticles with a high stability in time by controlling the variable molar ratio concentration between protective and reducing agents [30] This weak polyelectrolyte (PAA) presents carboxylate and carboxylic acid groups at a suitable pH, being of great interest for the synthesis of metal nanoparticles. The carboxylate groups of the PAA can bind silver cations, forming positively charged complexes, and a further reduction of the complexes to silver nanoparticles takes place [31,32,33]
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